There have been various distractor systems developed, many of which in one form or another utilize a plurality of transfixing and/or half pins which extend through the bone and outward beyond the soft tissue surrounding the bone. The multiple pins are positioned on opposite sides of the fracture and rigidly attached to one or more pin couplings at their distal ends. The pin couplings are interconnected by at least one mounting bar which permits the bone portions located on opposite sides of the fracture to be repositioned relative one another. It is often necessary during surgery to repair broken, deformed or damaged bones and joints to distract tissue segments of interest to provide the proper alignment prior to positioning fixation elements. The distractors that must be utilized to overcome deforming compressive forces of contracted soft tissue may interfere with access to the surgical site in several ways. From a mechanical standpoint, the distraction frame may obstruct physical access to the patient's wound. Furthermore, from a visualization standpoint, the distraction frame may obstruct the surgeon's ability to see the surgical site and the ability to visualize the underlying tissue using X-ray imaging or other devices.
One example of prior art is disclosed in U.S. Pat. No. 4,220,146 to Cloutier, which is incorporated by reference into this Application in its entirety. Such a prior art distractor is illustrated in FIG. 1. The prior art distractor comprises an upper pin 102 which is introduced laterally through a patient's bone above a joint, for instance, into the femoral condyles 104a and 104b in a direction perpendicular to the long axis of the femur according to well known surgical procedures. A lower pin 106 is introduced laterally below the joint into the patient's tibia 108 through the soft tissue of the bone in a direction substantially parallel to that of the upper pin 102.
The upper and lower pins 102 and 106 are connected to each other on both sides of the femur 107 and tibia 108 by a pair of threaded rods 110a and 110b. Mounted to the threaded rod 110a, is a serrated wheel 112a. One leg 116a of an L-shaped member 114a is rotatedly coupled to the wheel 112a. The other leg 118a of the L-shaped member couples to the pin 106. The leg 118a is pierced by a cylindrical hole extending along its longitudinal axis. The cylindrical hole is of such a diameter as to receive a portion of the rod 110a in a slidable manner and to guide the same. In a similar manner, an L-shaped member 114b and wheel 112b couple the pin 106 to threaded rod 110b. 
Adjustments in the vertical distance between the pins 102 and 106 can be made by turning the wheels 112a-112b along the threaded rods 110a and 110b. After the pins 102 and 106 are in place, turning the wheels 112a and 112b in a downward manner will induce compression stresses within the threaded rods 110a and 110b. 
Because the rods 110a and 110b are relatively slender, the rods flex or buckle under compressive stresses. The buckling causes additional flexural stressed to develop within the rods. Furthermore, threads surrounding the exterior of the threaded rods 110a and 110b reduce the effective cross-sectional area of the rods and introduces residual stresses from threading process which further reduces the rod's structure strength.
Thus, there exists a substantial need for an improved distraction device adapted for intra-operative use.